Duplex Filter

Advantages of the duplex strainers

During normal operations the strengths of the duplex filter is that it can be completely operated maintenance-free, except for checking the seals and cleaning of the filter element. With two filter chambers connected with a changeover valve one chamber is always in operation while a clean filter chamber is in standby mode. Duplex filters are primarily used where shutting down machines and systems are not practical or highly uneconomical, for example, in the maritime or the production industry.

How the duplex strainer works:

Filtration phase

While one filter chamber of the duplex strainer is in filtering mode, the other chamber is always with a cleaned filter element off line. The liquid passes through the filter element and over time the pressure drop in this filter chamber will increase. The increased pressure drop is an indication that particles have been accumulated and cleaning is required. Optional a differential pressure indicator can be installed on the duplex strainer.

Cleaning phase

By activating the switch plug, the clean filter chamber will be put in operation and the dirty filter chamber is simultaneously switched off. Switching to the clean filter chamber is carried out without a pressure surge.

For cleaning, the contaminated filter chamber is depressurized by the vent screw, the housing cover is
removed and the filter element has to be removed. The filter element is cleaned by flushing it with a cleaning fluid and subsequently blown out using compressed air.

Duplex Filter from BOLLFILTER

BOLLFILTER Duplex Type 2.04.5: Nodular cast iron filter with plug change over valve for small volumes »

Flange Connection: DIN Only DN 25 - DN 80 (Approx. 1" - 3")
Switch-over: plug valve
Filter element: star-pleated element, basket element

BOLLFILTER Duplex Type 2.05.5: Nodular cast iron filter with plug change over valve for large volumes »

Flange Connection: DIN Only DN 100 - DN 250 (Approx. 4" - 10")
Switch-over: plug valve
Filter element: basket element, ring element, filter candle insert, multi-mantle element

BOLLFILTER Duplex Type 2.68.2 / 2.78.2: Welded filter with ball change over valve and flexible connections »

Flange Connection: ASME or DIN 2 ½" - 14" DN 65 - DN 350
Switch-over: ball valve Change over (optional as with Butterfly valves)
Filter element: cleanable (stainless steel element), disposable (glass-fiber matting)

BOLLFILTER Duplex Type BFD: Cast filter with ball change over valve »

Flange Connection: ASME or DIN 1" - 6" / DN 25- DN 150
Switch-over: ball valve
Filter element: candle or basket element

BOLLFILTER Duplex Type BFD-P HD: particle gas filter for Heavy Duty »

Flange Connection: ASME or DIN ¾” – 8” or DN 20 – DN 200
Filter element: Fiberglass/stainless steel disposable cartridges* Cleanable elements (star-pleated) made of stainless steel
Grade of filtration: 0,5 - 250 µm

BOLLFILTER Duplex Type BFD-C HD: coalescer gas filter for Heavy Duty »

Features: Duplex filter for separating solids and aerosols (liquid content) from gases
Flange Connection: ASME or DIN ¾” – 8” or DN 20 – DN 200
Filter element: Fiberglass/stainless steel disposable cartridges (as normal temperature and high/low temperature design); Option available for preliminary separation using demister, cyclone, or cyclone demister all within the same housing.

BOLLFILTER Duplex Type BFD-C/P DBB: coalescer and particle gas filter with Double Block and Bleed »

Features: A special design duplex filter for separating solids and/or aerosols (liquid content) from gases using a patented double block and bleed main transfer valve. This is intended for applications using high pressures and/or dangerous gas compositions, to ensure maximum operator safety.
Flange Connection: ASME or DIN ¾” – 8” or DN 20 – DN 200
Filter element: Fiberglass/stainless steel disposable cartridges* Option available for preliminary separation using demister, cyclone, or cyclone demister all within the same housing